Diatom communities inhabiting intertidal estuarine sediments are composed of different life-forms, ranging from adnate epipsammic to free-living epipelic and tychoplanktonic forms. A detailed study of the spatial and temporal distribution patterns of various life-forms in the macro-tidal Westerschelde estuary (South-West Netherlands) revealed that the specific life-form composition of a community has an important influence on its temporal dynamics and might also have major implications for the transfer of diatom-fixed carbon to higher trophic levels. The importance of substrate structure and availability, stochastic (e.g. climate-induced and anthropogenic) hydrodynamic events and the nature and rate of sediment development in regulating the dynamics of these communities are evaluated

Hamels, I.

Muylaert, K.

Sabbe, K.

Vyverman, W.

Open Marine Archive

(representative) num ber o f individuals should be analysed and appropria­
te statistical analyses should be used to test for significant differences 
between varieties.
At present a big num ber of fingerprinting techniques exists to detect 
diversity at the DNA level. Two techniques, AFLP (Amplified Fragment 
Lenght Polym orphism ) and SSR (Simple Sequence Repeats), which have 
proven to be very useful for the screening of polymorphisms among a set 
of individuals are used at the Departm ent o f Applied Plant Genetics and 
Breeding. These two techniques differ in multiplex ratio (number of loci 
that are screened in a single reaction) and in information content (num­
ber of alleles that can be detected per marker in a set of individuals, 
Rafalski et al. 1996). AFLP has a higher multiplex ratio, while SSR 
mark-ers have a higher information content.
It will be presented in which way the m olecular fingerprinting techni­
ques are being applied at the Departm ent o f Applied Plant Genetics and 
Breeding for the evaluation of genetic diversity. The applications that will 
be presented can be divided into two main groups : i) germplasm analy­
sis in ryegrass and azalea and ii) description and identification of com ­
mercial varieties of ryegrass, sugar beet and azalea. AFLP has already 
been successfully used for all the applications mentioned above, while 
SSR is still under developm ent for ryegrass and azalea.
Ecological implications of life-forms in 
intertidal benthic diatoms in macrotidal estuaries^m-HV
Koen S a b b e , Wim V y v e r m a n , Koenraad M u Y L A E R t  & Ilse H a m e l s
University o f  Gent, D epartm ent o f  Morphology, Systematics & Ecology,
Section Protistology and Aquatic Ecology, K.L. Ledeganckstraat 35,
B-9000 Gent, Belgium
Diatom com m unities inhabiting intertidal estuarine sediments are 
com posed of different life-forms, ranging from adnate epipsammic to 
free-living epipelic and tychoplanktonic forms. A detailed study of the 
spatial and temporal distribution patterns of various life-forms in the 
macro-tidal W esterschelde estuary (South-W est Netherlands) revealed
170
that the specific life-form composition of a com m unity has an important 
influence on its temporal dynamics and might also have major im plica­
tions for the transfer of diatom-fixed carbon to higher trophic levels.
The importance of substrate structure and availability, stochastic (e.g. 
climate-induced and anthropogenic) hydrodynamic events and the nature 
and rate of sediment development in regulating the dynamics of these 
communities are evaluated.
Does reedbed mowing bottleneck Lipara lucens 
populations ?
M. S a n t e n s , L. D e  B r u y n  & R. V e r h a g e n
University o f  Antwerp (RUCA), Departm ent o f  Biology,
Evolutionary Biology Group 
E-mail : santens@ ruca.ua.ac.be
The fragmentation of reedbeds, the home of the gall-forming Phrag­
mites parasite Lipara lucens, results in a system o f metapopulations with 
frequent extinctions and recolonizations. M oreover large reedbeds are 
frequently mown for conservation purposes which also results in com ­
plete are almost complete population extinction. To investigate the effects 
of such events on the genetic com position o f affected populations, we 
caused artificial extinctions in five L. lucens populations near Antwerpen. 
This was done by mowing the reedbeds in late winter with removal of the 
litter and with it the L. lucens galls. All five reedbeds were recolonized by 
L. lucens in the generation following the artificial extinction. The genetic 
consequences o f these events were studied by comparing the genetic 
composition, assessed by way of allozyme electrophoresis, of the native 
and the founder population. Generally, it is assumed that when a popula­
tion goes through a bottleneck, genetic variability decreases.
Reduction in genetic diversity (expected heterozygosity) was only 
found in the smallest population. The other examined populations show­
ed an increase in genetic diversity. Moreover, some rare alleles, not found 
in the native populations were gained after the founder event while other
171


Ecological implications of life-forms in intertidal benthic diatoms in macrotidal estuaries

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